The present invention relates to a method and apparatus for controlling the sex of mammalian offspring by separation of X-chromosome female producing sperm of a certain density and electric potential from Y-chromosome male producing sperm of a differing density and electric potential.
As discussed in the aforementioned applications, the sex of offspring is controlled by the chromosomes of the particular sperm cell which fertilizes the egg. As further disclosed therein, X-chromosome-containing sperm which are responsible for producing female offspring are somewhat more dense than Y-chromosome-containing sperm which are responsible for producing male offspring. Additionally, it has been determined that X and Y-chromosome-containing sperm have a differing electric potential on their respective cell surfaces. These differences in density and electric potential make possible the separation of sperm into fractions containing substantially all of either the X or the Y sperm. Separation techniques utilizing these density and electric potential differences are suitable for use with all mammals including human beings and other primates, cattle, swine, sheep, rabbits, cats, dogs, goats, horses, donkeys, buffalo, etc. As previously disclosed, primarily in application Ser. No. 443,473, the method of separation by density has been to apply a buoyant force to the sperm to cause the more buoyant sperm to attain a different level in the separation medium than the less buoyant sperm where the buoyant force applied has been either positive or negative or both. As previously practiced, the separation of X and Y sperm cells by differing electric potential has been difficult due to the fact that while in the seminal fluid the positive and negative zeta potential of the female and male spermatozoa create an equilibrium within the dielectric constant of the medium thus making it difficult to draw them apart in a galvanic field. This equilibrium has been mainly due to the substantially equal populations of X and Y cells of opposite charge which have been subjected to this process. While various types of electrophoreses cells have been utilized in the attempt to separate male and female spermatozoa with applied potentials varying from 200 microvolts to 10 volts DC, the outcome has been disappointing particularly when the concentration of separated cells was too low to achieve a fair conception. The use of higher current while possibly increasing the purity of the separation has been found to lower the viability of the sperm. These problems have been substantially overcome in the present invention where sperm fractions containing substantially unbalanced populations of X and Y cells resulting from a first separation by thermal convection counter streaming sedimentation are placed in a forced convection column maintained between the two electrodes of an electrophoreses cell thus causing the respective cells of different charge to be preferentially drawn to their respective electrodes in a more efficient manner than heretofore obtained.
It has been noted in the past that the presence of foreign particles in the medium disturbs both the buoyant or sedimentation velocity of the sperm and their movement due to galvanic forces as well as their fertilization capacity after separation. The use of the universal medium disclosed in U.S. Pat. No. 3,816,249 substantially eliminates this problem while promoting control of cellular hyperactivity and prolonging sperm life as well. The use of the universal medium as well as the imposition of a low temperature immobilizing the sperm prevents the small difference in density (2 to 5%) and electric cell surface potential between male and female sperm from being neutralized by the high metabolic activity of the sperm cells.